Assign Game ID to WP Post

I need a small Wordpress Plugin coded, which assigns a Items ID (f.e. book_id) to a Wordpress Post. This means, when creating or editing a WP Article inside the Wordpress Admin Interface, there must be a dropdown Box, which displays all available Items that can be assigned. The Items inside the dropdown Box must be dynamically pulled out of another Database Table, since these get added/removed by another Script outside Wordpress. Example Database Table which will be used: book_id (int) book_name Assigning a book to an Article must be "optional". When you got the Plugin working, I need a Simple Demo Page that shows me how to Access the book_id inside the Article Page, so I can pull all other "book" Informations out of my Database.